A multiphase CFD model of DAF process

Ta, C. T.; Beckley, J.; Eades, A.

doi:10.2166/wst.2001.0488

Cited by 42 publications

(19 citation statements)

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“…Multiphase computational fluid dynamics (CFD) models have been applied to optimize tank geometry and flow of water with suspended gas and flocs inside the tank (Ta et al, 2001). The general flow pattern has been compared with flow visualization using the underwater cameras and various soluble and insoluble dyes (green, red etc.).…”

Section: Advances In Daf Design For Industrial Wastewater Pretreatmentmentioning

confidence: 99%

New Developments in Mixing, Flocculation and Flotation for Industrial Wastewater Pretreatment and Municipal Wastewater Treatment

Čolić¹,

Morse²,

Morse³

et al. 2005

proc water environ fed

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Solid/liquid separations are commonly the first step in any wastewater treatment. Such technologies are mature and new developments are rare. However, in the last decade some significant improvements in separation techniques for industrial wastewater pretreatment have been implemented. Advances in the technology include more efficient, faster centrifugal mixing of treatment chemicals and wastewater contaminants, "in situ" continuous flow coagulation and flocculation, implementation of very high molecular weight flocculants and development of more efficient flotation technologies. Recent developments and improvements of commonly used dissolved air flotation units along with development and application of centrifugal flotation units, cavitation air flotation and suspended air flotation will be discussed. Case studies are also described. Hybrid centrifugal -dissolved air flotation technologies provide the best of both systems: efficient continuous flow mixing and in line flocculation with the nucleation and entrainment of fine dissolved air bubbles. This development has resulted in systems with very efficient removal of particulate contaminants, a small footprint, drier sludge, durable long lasting flocs, fast response and treatment of the total wastewater stream (no recycling characteristic for DAFs). The design of on-line turbidity driven sensors for automatic control of coagulant and flocculant dosage is also underway. Computational fluid dynamics (CFD) has been used to design better flotation tanks with a vortical flow pattern that results in the formation of a dense air bed inside the tank. Such fine bubble layers prevent sedimentation of already floated heavier particulates, which results in significantly higher flotation rates.

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Section: Advances In Daf Design For Industrial Wastewater Pretreatmentmentioning

confidence: 99%

New Developments in Mixing, Flocculation and Flotation for Industrial Wastewater Pretreatment and Municipal Wastewater Treatment

Čolić¹,

Morse²,

Morse³

et al. 2005

proc water environ fed

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show abstract

“…Moreover, Ta et al (2001) have modelled the multiphase flow in both contact zone and separation zone and validated the results using ADV measurements. Considering complexities involved in multiphase flow simulations results could just be confirmed qualitatively.…”

Section: Similar Projectsmentioning

confidence: 96%

Dissolved Air Flotation

Parsons

Jefferson

2006

Introduction to Potable Water Treatment Processes

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One of the well known intermediate stages to treat water and wastewater is Dissolved Air Flotation (DAF). In order to design an efficient DAF unit, it is important to study the system and get familiar with the flow structure in it. Computational Fluid Dynamics (CFD) is used as a tool to study a flotation unit.Most of the previous CFD studies of DAF have been set up in two dimensions in order to reduce the required computational time and space. By modeling only in two dimensions the effects of the flow from the needle valves is excluded. This study aims to consider these effects through three-dimensional modeling. The aim is to study the contact zone considering variables affecting this part of the DAF unit. These variables are number of needle valves, tank geometry, side wall effects and presence of the separation zone.In this study two-and three-dimensional representations of the tank are evaluated. Simulations account for both one-phase and two-phase flow and the flow is assumed to be in steady state. The geometry of the tank is modeled in GAMBIT and exported to FLUENT 12 to perform the flow simulations. The flow in the tank is assumed to be turbulent, which is modeled with the standard and the realizable k-ε models. Standard wall function and non equilibrium wall functions are used for these models respectively. The Lagrangian model is used to simulate the two-phase flow consisting of air bubbles and water. Validation of the results is made by comparing the simulated flow with previously measured flow patterns in a pilot DAF tank.Results show that convergence is very connected to the outlet location and the further away the outlet is located from the contact zone the easier it is to reach a converged solution. The number of needle valves included in the model and the inclusion of the side walls are parameters found to have an effect on the flow structure in contact zone. The two-phase flow result predicts a movement of air bubbles toward the inlet zone a phenomenon not observed in the experimental measurements.

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“…Many efforts have been made, generally using particle tracking method (Saul and Stevin [14]), but when there is a strong coupling between fluid flow and the secondary phase, Eulerian-Eulerian multiphase model is more suitable (Ta et al [16]). …”

Section: Introductionmentioning

confidence: 99%

Methodology to determine residence time distribution and small scale phenomena in settling tanks

Karches¹,

Buzás²

2011

Computational Methods in Multiphase Flow VI

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Hydraulic residence time is a crucial parameter of any wastewater treatment tank planning, operation and optimisation. Calculation of the residence time distribution at every point within the tank gives information about the deadzones and short circuits and well-operating zones. Using the advective-diffusive transport equation supplemented with a scalar source term local mean age (LMA) can be detected if the flow field is given. Combining LMA with a tracer study the exact residence time can be determined. This method supports problem detection in a small wastewater treatment plant (2 dead zones and one shortcircuiting path were detected) and also gave us better understanding of the operation of settling tanks.

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A multiphase CFD model of DAF process

Cited by 42 publications

References 0 publications

New Developments in Mixing, Flocculation and Flotation for Industrial Wastewater Pretreatment and Municipal Wastewater Treatment

New Developments in Mixing, Flocculation and Flotation for Industrial Wastewater Pretreatment and Municipal Wastewater Treatment

Dissolved Air Flotation

Methodology to determine residence time distribution and small scale phenomena in settling tanks

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